In the related art, the water filtration system only uses a one-stage filter membrane to filter water and hence the water is not processed by fine filtration, so the filter effect is not ideal and physical health will be influenced in the case of drinking the water directly. In the related art, the water filtration system adopting a multi-stage filter cartridge has disadvantages of a complicated pipeline, too many joints and a large volume. In addition, waste is caused when pure water obtained after being processed by the multi-state filter cartridge serves as domestic water for cleaning clothes, taking showers and watering flowers. Furthermore, waste water produced in the filtration process is discharged directly, which has a low utilization rate, thus causing waste of water resources.